An avalanche process is typically used in semiconductor devices for photon-sensing applications. In general, the avalanche process can be triggered when a p-n junction is reversely biased under a corresponding breakdown voltage. In particular, to detect light signals with very weak intensities, the p-n junction is biased above the breakdown voltage, which is typically known as operating under a Geiger mode. A photon-sensing device that operates under the Geiger mode is generally known as a single photon avalanche diode (SPAD).
Such SPADs have been widely used in various devices such as, for example, cameras of handheld devices. Although these SPADs have proven useful, there remains room for improvement. For example, a problem suffered by existing SPADs is that their photon detection possibility (PDP) is subjected to a maximum wavelength (e.g., a blue light wavelength), because incident light with longer wavelengths (e.g., a near infra-red (NIR) light wavelength) is typically blocked by a plurality of interconnection layers (e.g., metal/dielectric layers) formed above the active regions of the existing SPADs. Thus, existing SPADs are not entirely satisfactory.